One way of simplifying the use of various types of appliances which are protected by, for example, passwords, access codes and the like, is to replace the codes with devices which recognize the user on the basis of different physical characteristics, so called biometry. One type of biometrical characteristic is fingerprint information, which can be used to test and either confirm or reject a user's attempt to gain access to an appliance, a premises, etc., referred to as user identity verification. Verification with the aid of fingerprint information is in most cases done by the user having stored his fingerprint information in the equipment in question in advance, by which means a template is created. The information for creating this template can either be input into the appliance which the user will later want to have access to, or via a central appliance.
When the user attempts to gain access to the equipment in question, a biometry device inputs information from the user's finger and compares the input information to the template in order to decide if the user is to be granted access to the equipment or not.
Equipment which verifies with the aid of fingerprint information must satisfy a number of requirements, for example reliability and speed. For verification to take place in portable devices, for example mobile telephones, portable computers, different types of cards, etc., the equipment must additionally be as small, lightweight and energy-efficient as possible. It is of course also a requirement that the equipment should be as inexpensive as possible. These requirements would also, naturally, improve devices for registering said reference information.
Known types of devices for verifying a user's identity with the aid of fingerprint information read information from a user's fingerprint and compare this with a template by means of the input information being combined into a representation of the fingerprint, which is then compared with the template which has been stored in advance. A disadvantage of such types of equipment is that they require a great deal of memory, on account of the representation of the fingerprint which is built up. This is also a drawback of know devices for registering said reference information. Memory is expensive, takes up space and requires a great deal of current, which means that known devices are relatively expensive and large.
Another parameter which affects cost and takes up space is the surface area of the sensor which is used to read the fingerprint information for the verification. This surface area can be reduced by using what is referred to as a line sensor, in other words a sensor whose surface area is too small to read a complete fingerprint without the finger and the sensor moving relative to each other. During verification or registering with the aid of such a sensor, the finger is moved relative to the sensor, and the abovementioned representation of the fingerprint is built up in a memory on the basis of consecutively input partial areas. Thus, line sensors satisfy the requirements regarding the size and cost of the actual sensor, but the requirement for memory remains. Using a line sensor, the equipment must be able to read information from a moving finger, as distinct from equipment which uses surface-area sensors, against which the finger is simply placed or held.
One example of prior art is SE 515 239, which deals with a method for assembling a composite image of a fingerprint, using a sequence of partial images. This document appears to deal exclusively with assembling an image of, for example, a fingerprint, and suffers from, inter alia, the abovementioned drawback of a large need for memory space.